The present invention relates to a rotary compressor, e.g., a slidable vane compressor or a Wankel-type rotary piston compressor, and more particularly to a rotary compressor improved in cylinder structure.
In general, a slidable vane compressor has a cylindrical rotor and a cylinder slidably contacting the rotor at one or more portions thereof. The cylindrical rotor has a plurality of substantially radial slits each movably receiving a slidable vane. The cylinder is closed at both its axial ends by respective side plates so that compression chambers are defined by the vanes, the cylinder and the side plates. In operation, as the rotor is rotated by a torque applied thereto, the volumes of the compression chambers are changed to compress a fluid.
In the conventional slidable vane compressor, since the tips of the slidable vanes slide on an inner surface of the cylinder at high speed, the material for the cylinder is inconveniently restricted to iron-based metals. Accordingly, the manufacture of the conventional cylinder is such that the cylinder is integrally formed from a cast iron, followed by a polishing of the inner surface thereof.
It has been known that, as discharge valves for the slidable vane compressor of this kind, such discharge valves are employed and can be inserted into axial openings parallel to the axis of the cylinder (the valve will be referred to as an "axial insert type discharge valve", hereinafter). The employment of the axial insert type discharge valve eliminates the necessity to provide a discharge chamber of high pressure on the outer periphery of the cylinder, and makes it possible to prevent deformation of the cylinder due to a high pressure and prevent leakage of a fluid through the gap between the slidable vane tip and the cylinder inner surface resulting from the deformation. Moreover, it is possible to expect the cylinder to be reduced in diameter and improved in its heat radiation performance. Rotary compressors having such axial insert type discharge valves have been disclosed in, for example, U.S. Pat. Nos. 4,088,428 and 4,149,843, and Japanese Patent Laid-Open No. 101093/81.
Since the cylinder in the conventional slidable vane compressors is a cast article made of an iron-based metal, however, it is difficult to form the axial opening for receiving the discharge valve and form a discharge bore for providing a communication between the compression chamber and the axial opening. More specifically, the discharge bore cannot be machined from the outside of the cylinder; hence, the discharge bore is conventionally machined from the inside of the cylinder by means of a special machine. In consequence, the discharge bore cannot be machined with a satisfactory accuracy, so that such a countermeasure has been required that a sleeve is separately provided to the axial opening to ensure the dimensional accuracy of the discharge bore, as seen in U.S. Pat. No. 4,149,834.
On the other hand, it has been known to provide a rotary compressor having a discharge valve exposed to the outside of the cylinder. In the design of such rotary compressors, it is often attempted to reduce the cylinder weight by adopting a composite cylinder structure consisting of an inner cylinder made of an iron-based metal and an outer cylinder made of a cast light metal enclosing most part of the outer peripheral surface of the inner cylinder to allow a part of the inner cylinder to be revealed through the outer cylinder, as shown in, for example, Japanese Patent Laid-Open No. 31689/1981. This rotary compressor cannot offer the above-mentioned advantage of the rotary compressor having the axial insert type discharge valve although it has the cylinder of light weight.